The present invention relates to bioavailable sustained-release pharmaceutical formulations of analgesic drugs, in particular opioid analgesics, which provide an extended duration of effect when orally administered.
It is known in the pharmaceutical art to prepare compositions which provide for controlled (slow) release of pharmacologically active substances contained in the compositions after oral administration to humans and animals. Such slow release compositions are used to delay absorption of a medicament until it has reached certain portions of the alimentary tract. Such sustained-release of a medicament in the alimentary tract further maintains a desired concentration of said medicament in the blood stream for a longer duration than would occur if conventional rapid release dosage forms are administered.
Slow release formulations known in the art include specially coated pellets, coated tablets and capsules wherein the slow release of the active medicament is brought about through selective breakdown of the coating of the preparation or through compounding with a special matrix to affect the release of a drug. Some slow release formulations provide for related sequential release of a single dose of an active compound at predetermined periods after administration.
It is the intent of all sustained-release preparations to provide a longer period of pharmacologic response after the administration of the drug and is ordinarily experienced after the administration of the rapid release dosage forms. Such longer periods of response provide for many inherent therapeutic benefits that are not achieved with corresponding short acting, immediate release preparations. This is especially true in the treatment of cancer patients or other patients in need of treatment for the alleviation of moderate to severe pain, where blood levels of an opioid analgesic medicament must be maintained at a therapeutically effective level to provide pain relief. Unless conventional rapid acting drug therapy is carefully administered at frequent intervals to maintain effective steady state blood levels of the drug, peaks and valleys in the blood level of the active drug occur because of the rapid absorption, systemic excretion of the compound and through metabolic inactivation, thereby producing special problems in maintenance of analgesic efficacy.
The prior art teaching of the preparation and use of compositions providing the sustained-release of an active compound from a carrier is basically concerned with the release of the active substance into the physiologic fluid of the alimentary tract. However, it is generally recognized that the mere presence of an active substance in the gastrointestinal fluids does not, by itself, insure bioavailability.
In order to be absorbed, the active drug substance must be in solution. The time required for a given proportion of an active substance from a unit dosage form is determined as the proportion of the amount of active drug substance released from a unit dosage form over a specified time base by a test method conducted under standardized conditions. The physiologic fluids of the gastrointestinal tract are the media for determining dissolution time. The present state of the art recognizes many satisfactory test procedures to measure dissolution time for pharmaceutical compositions, and these test procedures are described in official compendia world wide.
Although there are many diverse factors which influence the dissolution of drug substance from its carrier, the dissolution time determined for a pharmacologically active substance from the specific composition is relatively constant and reproducible. Among the different factors affecting the dissolution time are the surface area of the drug substance presented to the dissolution solvent medium, the pH of the solution, the solubility of the substance in the specific solvent medium, and the driving forces of the saturation concentration of dissolved materials in the solvent medium. Thus, the dissolution concentration of an active drug substance is dynamically modified in its steady state as components are removed from the dissolution medium through absorption across the tissue site. Under physiologic conditions, the saturation level of the dissolved materials is replenished from the dosage form reserve to maintain a relatively uniform and constant dissolution concentration in the solvent medium providing for a steady state absorption.
The transport across a tissue absorption site of the gastrointestinal tract is influenced by the Donnan osmotic equilibrium forces on both sides of the membrane since the direction of the driving force is the difference between the concentrations of active substance on either side of the membrane, i.e., the amount dissolved in the gastrointestinal fluids and the amount present in the blood. Since the blood levels are constantly being modified by dilution, circulatory changes, tissue storage, metabolic conversion and systemic excretion, the flow of active materials is directed from the gastrointestinal tract into the blood stream.
Notwithstanding the diverse factors influencing both dissolution and absorption of a drug substance, a strong correlation has been established between the in-vitro dissolution time determined for a dosage form and (in-vivo) bioavailability. The dissolution time and the bioavailability determined for a composition are two of the most significant fundamental characteristics for consideration when evaluating sustained-release compositions.
It has previously been known in the art that sustained-release compositions of opioids or salts thereof could be prepared in a suitable matrix. For example, in U.S. Pat. Nos. 4,990,341 and 4,844,909 (Goldie, et al.), both assigned to the assignee of the present invention, describes hydromorphone compositions wherein the dissolution rate in vitro of the dosage form, when measured by the USP Paddle or Basket Method at 100 rpm in 900 ml aqueous buffer (pH between 1.6 and 7.2) at 37.degree. C., is between 12.5 and 42.5% (by wt) hydromorphone released after 1 hour, between 25 and 55% (by wt) released after 2 hours, between 45 and 75% (by wt) released after 4 hours and between 55 and 85% (by wt) released after 6 hours, the in vitro release rate being independent of pH between pH 1.6 and 7.2 and chosen such that the peak plasma level of hydromorphone obtained in vivo occurs between 2 and 4 hours after administration of the dosage form. At least 12 hours of pain relief is obtained with the hydromorphone formulations.
Once-a-day orally administrable dosage forms have previously been developed in the art and are commercially available. However, currently, there are no orally administered opioid formulations commercially available which provide an extended duration of effect, e.g., greater than about 12 hours. Examples of commercially available once-a-day dosage forms include Dilacor.RTM. XR (diltiazem hydroxide, extended-release capsules, available from Rhone-Poulenc Rorer), Thorazine.RTM. Spanule.RTM. (chlorpromazine HCl, extended-release capsules, available from SmithKline Beecham), Theo-24.RTM. (theophylline, extended-release capsules, available from Searle), TheoX.RTM. (theophylline, extended-release tablets, available from Carnrick), Theo-dur.RTM. (theophylline, extended-release tablets, available from Key), Theo-Sav.RTM. (theophylline, extended-release tablets, available from Sauage), Uniphyl.RTM. Unicontin.RTM. (theophylline, extended-release tablets, available from Purdue Frederick), T-Phyl.RTM. Unicontin.RTM. (theophylline, extended-release tablets, available from Purdue Frederick), Tenuate Dospan.RTM. (diethylpropion HCl, extended-release tablets, available from Marion Merrill Dow), Tepanil.RTM. Ten-Tab.RTM. (diethylpropion HCl, extended-release tablets, available from 3M Riker), Desoxyn.RTM. Gradumet.RTM. (phenmetrazine HCl, extended-release tablets, available from Abbott), Dexedrine.RTM. Spanule.RTM. (dextroamphetamine, extended-release capsules, available from SmithKline Beecham), Compazine.RTM. Spanule.RTM. (prochlorperazine maleate, extended-release capsules, available from SmithKline Beecham), Indocin.RTM. SR (indomethacin, extended-release capsules, available from Merck), Betachron.RTM. (propranolol HCl, extended-release capsules, available from Inwood), Inderal.RTM. LA (propranolol HCl, extended-release capsules, available from Wyeth-Ayerst), Inderide.RTM. LA (propranolol HCl and hydrochlorothiazide, extended-release capsules from Wyeth-Ayerst), Procardia XL.RTM. (nifedipine, extended-release tablets, available from Pfizer), Mestinon.RTM. Timespan.RTM. (pyridostigmine Br, extended-release tablets, available from ICN), Temaril.RTM. Spanule.RTM. (trimeprazine tartrate, extended-release capsules, available from Herbert), AL-R.RTM. 6 (chlorpheniramine maleate, extended-release capsules, available from Saron), Chlor-Trimeton.RTM. Allergy Repetabs.RTM. (chlorpheniramine maleate, extended-release tablets, available from Schering-Plough), Adipost.RTM. (phendimetrazine tartrate, extended-release capsules, available from Ascher), Bontril.RTM. Slow-Release (phendimetrazine tartrate, extended-release capsules, available from Carnrick), Melfiat.RTM.-105 Unicelles.RTM. (phendimetrazine tartrate, extended-release capsules, available from Solway), Prelu-2.RTM. (phendimetrazine tartrate, extended-release capsules, available from Boehringer Ingelheim), PT 105.RTM. (phendimetrazine tartrate, extended-release capsules, available from Legere), Wehless.RTM.-105 Timecelles (phendimetrazine tartrate, extended-release capsules, available from Hauck), Preludin.RTM. Endurets.RTM. (phenmetrazine HCl, extended-release tablets, available from Boehringer Ingelheim), Caffedrine (caffeine, extended-release capsules, available from Thompson), Diamox.RTM. Sequels.RTM. (acetazolamide, extended-release capsules, available from Storz), Verelan.RTM. (verapamil HCl, extended-release capsules cont. pellets, available from Wyeth-Ayerst), Calan.RTM. SR Caplets.RTM. (verapamil HCl, extended-release tablets, available from Searle), Isoptin.RTM. SR (verapamil HCl, extended-release tablets, available from Knoll), Verapamil HCl Tablets (verapamil HCl, extended-release tablets, available from GoldLine), and Artane.RTM. Sequels.RTM. (trihexyphenidyl HCl, extended-release capsules, available from Lederle).
There is a need in the art to develop drug formulations which provide a duration of effect lasting longer than twelve hours such as a drug that may be administered to a patient only once a day. Many of the oral opioid analgesic formulations that are currently available in the market must be administered every four to six hours daily with a selected few formulated for less frequent 12 hour dosing.
Morphine, which is considered to be the prototypic opioid analgesic, has been formulated into 12 hour controlled-release formulations (i.e., MS Contin.RTM. tablets, commercially available from Purdue Frederick Company).
An orally administrable opioid formulation which would provide an extended duration of effect would be highly desirable. Such an oral sustained-release formulation of an opioid analgesic would provide effective steady-state blood levels (e.g., plasma levels) of the drug when orally administered such that a duration of effect greater than 12 hours, and more preferably, of about 24 hours or more, which formulation is bioavailable as well.